1. Field of the Invention
It is known that in order to facilitate the connection of coils, and particularly of enameled copper wire coils, in electronic circuits, when manufacturing the coils themselves one provides to carry out the tinning of the terminals.
2. Description of the Prior Art
Two techniques are essentially provided for this purpose.
According to a first known system, the tinning of the terminals is carried out when the coil is already fully wound. In this case, the enameled copper terminals project tangentially from the coils and it is possible to immerge them into a melted tin bath; the temperature of the bath is such that it will destroy the enamel coating, thus allowing a perfect tinning.
It is however not always possible or appropriate to use this technique; if the terminals are very short, the immersion in the tin bath becomes in fact difficult, or even impossible if the tinning level is higher than the tangency to the coil body. In other cases, and particularly with terminals coming out tangentially in different directions, this tinning operation has to be carried out in two stages and thus becomes too long.
Another technique consists instead in carrying out the tinning along the copper wire coming from the feeding reel, and precisely in correspondence of positions which will then coincide with the position of the terminals, once the wire has been wound.
A known device allowing to carry out such tinning on a running length of copper wire, is based on the concept of letting the copper wire normally slide in close proximity of a melted tin bath, and then -- in the position and at the moment of carrying out the tinning -- causing a wave to be formed in said bath, which, upon rising, will lap the wire, thus carrying out the tinning thereof. Nonetheless, in general, this device does not provide sufficient reliability of work; moreover, the length of time in which the tin bath remains in contact with the wire is usually too short to surely destroy the enamel layer.
A further known device for carrying out this type of tinning comprises a rectilinear path of the copper wire over a melted tin bath, and a spoon normally immerged in said bath, said spoon -- at the moment of the tinning -- raising a small quantity of melted tin. The spoon has, on its opposed side walls, two slits which are sufficiently narrow to prevent the melted tin from coming out of said slits, thanks to a superficial tension effect. When the spoon is raised, filled with melted tin, the copper wire engages into said slits and is hence immerged in the melted tin; the tinning is then carried out over a wire length equal to the spoon width. Nonetheless, also this device has its own drawbacks: first of all, if one had to modify the length of tinned wire, it would be necessary to replace the spoon; moreover, since the wire is drawn out of the bath exactly in the same position in which it is immerged, it so happens that the scruff formed by the enamel having come off the wire easily falls back again onto the wire itself -- as the latter comes out of the bath -- and remains stuck thereon upon cooling of the tinning.
Finally, a rather serious drawback, common to the two above mentioned tinning devices, should further be mentioned. It happens in fact that, at the moment in which the melted tin mass, after having been brought into contact with the horizontal wire, abandons the latter at the end of the tinning stage -- both in the event of the wire being abandoned rapidly (as in the tin-wave device), and in the event of the wire being abandoned more slowly (as in the aforementioned spoon device) -- on the wire itself is formed, in a more or less central position, like a small tin drop. Upon cooling this drop forms a swell which provides two kinds of drawbacks: on the one hand, in fact, when the wire is fed to the wireguide of the coil winding machine, which has a minimum passage section, said swell may get caught into the wire-guide itself, eventually also causing the breaking of the wire; on the other hand, this swell is generally sufficient to prevent the correct insertion of the coil terminals into the holes of the printed circuits, on which the coil has to be mounted, said holes being in fact usually small.